The present invention relates to a friction stir welding method suitable for use in joining members of various materials, including, for example, aluminum alloy members.
A friction stir welding method is a method in which by rotating a round-shaped rod (a rotary body) inserted in a joining region between two members (e.g., but not limiting, two metal bodies, such as bodies each made of aluminum), and further by moving the rotary body along a joining line, the two bodies at the joining region are heated, and material thereof softened and plastically fluidized and thus the two bodies are solid-phase joined, e.g., are welded together at the joining region.
Conventionally, the rotary body comprises a small diameter portion which is inserted in the joining region and a large diameter portion which is positioned outside the joining region. The small diameter portion and the large diameter portion are positioned on the same axis. A side of the large diameter portion is rotated, whereby both the large and small diameter portions are rotated. A boundary portion between the small diameter portion and the large diameter portion can be inserted a little into the joining region. A joining according to the friction stir welding method can be applied to an abutting portion and an overlapping portion.
The above-stated prior technique is disclosed, for example, in Japanese patent announcement laid-open publication No. Hei 7-505090 (EP 0615480 B1); Dawes, “An Introduction to Friction Stir Welding and Its Development”, in Welding & Metal Fabrication (January 1995), pages 13, 14 and 16; and by U.S. patent application Ser. No. 08/820,231, filed Mar. 18, 1997, the contents of which are incorporated herein by reference in their entirety.
This prior technique is also described in the article by T. Shinoda and Y. Rondoh, “324 Butt Welding of Plate Using Friction Stir Welding; Method Study of Friction Stir Welding”, Welding Associate Japan Lecture Meeting Outline, No. 56 (April 1995), pages 208 and 209. This article discloses a rotary body (rotary tool) made of stainless steel, members to be welded (joined) made of pure aluminum (Al100), and the members to be welded having a plate thickness of 6 mm. The rotary body has a large diameter portion with a diameter of 20 mm, and a small diameter portion (cylindrical) with a diameter of 6 mm and a length (axially) of 5 mm. In operation, the rotary body rotates at 1000–2500 rpm, and moves along the two members to be welded at a speed of 1.0–8.0 mm/s.
In the article described in the foregoing paragraph, the members to be joined are made of aluminum. Alloys of aluminum are also suitable for welding by friction stir welding; other metals studied for welding by friction stir welding include copper, titanium and stainless steel. EP 0615480 BI, referred to previously herein, discloses friction stir welding of plastic (e.g., thermoplastic) materials. All of these materials can be welded by the process of the present invention.